Getting the XJ12 on the road

With this hot weather we are having in the Pacific Northwest (and my XJS in my shop addressing an oil leak that made a new if my engine bay I detailed last winter), I have a renewed interest in getting my seldom used XJ12 back on the road.

A few issues to sort out:

  1. There is a shudder. I just took it to the tire shop and they balanced the wheels (free of charge, nice of them). I took it for a drive after getting it back. It started out fine. Drove a couple miles on the interstate, exited, drove a couple miles on surface streets, got back on the interstate, and when I hit the brakes the shudder started again. And it’s not just when the brakes are applied, but that’s what starts it. I exited the freeway and continued getting a shudder whether or not the brakes were applied.

  2. “Trac Fail” and “Anti Lock” lights are on.

  3. Upon parking the engine temp crept up and there was a noticable amount of coolant on the ground. It was coming for the bottom side of the header tank (atmospheric catchment tank).

My thinking is

Front brake job for number 1.

Cleaning the wheel sensors for number 2.

And for what I’ve read on here, starting with a new call on the header tank for number 3.

If anyone has any further ideas, please let me know.

Is this an X305, or XJ40 style, or the pukka Series 1-3 XJ12?

(Edit: trac fail is a hint I guess :slight_smile: )

Check the wheel bearings too.

I have a 96 that needs a new front suspension. Looks like a huge job.

1996 x305.

I will take a look at the bearings too.

Hopefully it doesn’t come to a full suspension rebuild. I did the front end of my XJS, can’t be that much more complicated… I hope.

Thanks for the suggestion.

I would check the front calipers. I spent alot of money trying to solve the same problem on my Rolls Royce Silver Shadow. When driving the car (like yours), it would be silky smooth UNTIL I pressed the brake pedal a few times. After that, it drove terribly. Simple to check! Stop the car and touch the hubcap (rim) and see if one is very hot. With mine, the caliper was not releasing because of the brake hose not letting the brake fluid return to the reservior.

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Good thought about dodgy caliper. Pad wear will reveal all there.

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Thank you, Richard. That was along my line of thought. I was thinking maybe the rotors weren’t true and then the pads were being held a little too close (or progressively getting closer and closer with each press).

It may also be a bad brake disc, warping when it heats up when the brakes are applied. I had that once on my '86 XJ6. New discs and pads sorted it.

New calipers, rotors, and pads seems to have solved the shutter. I think it was the calipers primarily. And repacked the bearings.

Cleaning the wheel sensors have solved the anti-lock and Trac Fail lights.

I replaced the cap on the header tank. First drive after that it still dumped coolant out after I parked. The second drive it didn’t. Currently on the third drive testing the brakes and no coolant leaks yet.

If the overall coolant supply is overfilled, the excess will be expelled via a drain in the atmospheric catchment tank. The tank typically should be 1/2 full, after the coolant level stabilizes and is at ambient temps. It’s a one gallon tank, so it allows for that volume of expansion as the system coolant heats up during a drive, and flows into the atmo tank. As the system cools, that coolant is then drawn back out of the atmo tank. SD Faircloth

That would definitely be nice if it was just me overfilling it. I filled it to right in-between the min and max ridges inside the tank.

The last two times it was a half a gallon to get back to that point.

I let it barf out coolant until reached the point it’s happy, and then didn’t add more. As long as it doesn’t overheat, and the coolant level stabilizes, then the marked coolant level isn’t important to me. If the level falls completely and the car runs warm that’s another story.

Haven’t had a chance to stress the system since we’ve had record low temperature lately. Initially it was creeping up.

Warmer temperatures later this week and we’ll see what happens.

I see your 1996 XJ12 may not have the atmospheric catchment tank, as does the XJS earlier models of the V12. It ( the XJ12) only has the expansion tank (aka recovery tank). In your first post at item #3, you refer to the item as the header tank, and in parenthesis ( atmospheric catchment tank). The header tank is under the hood. The atmospheric catchment tank is hidden in a cubby hole covered with a cover plate, at the rear of the front left wheel well. Threw me off. SD Faircloth

Sorry, I thought I was using the correct terminology.

The coolant is coming from the bottom of the small tank on the top left side of the engine compartment.

I don’t have an XJ12, so I can only look at pics of a recovery tank. Nor can I find a decent hose routing diagram. If yours is leaking from the bottom, I fail to see how replacing the cap is going to resolve that. There is a hose that fits at the bottom of the tank, which I assume is the hose that routes (sucks) coolant back to the engine as it cools down. Possible source of your leak ? Also, yours may be cracked somewhere underneath ? Were it my vehicle, I would be removing the tank and hoses for a thorough inspection, albeit yours looks mighty clean. Also, don’t understand two hoses entering from the side. ? SD Faircloth

I was kind of going off this old post. Though header/recovery/atmospheric catchment are thrown around in this post, as well.

Maybe I’m misinterpreting this issue as similar to mine.

The coolant RESERVOIR and coolant RECOVERY TANK (‘atmoshperic catchment tank’)

are two different cooling system components.

The reservoir has a pressure cap and the recovery is open to the atmosphere.

Except…the parts diagram for the XJ12 calls the item in Jay’s photo a expansion tank AND a recovery tank on the same page. Hence, more confusion for some.

The earlier model V12’s call it a header tank or an expansion tank, and the item at the rear of the left wheel well…the atmospheric catchment tank. SD

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Plugging away. Rear rotor and pads. Top caliper bolt really put up a fight.